This invention relates to a protective means for preventing wear of the inner surface of a shell of a vertical pulverizer for pulverizing a material into powder or particles by stirring it with a pulverizing medium.
FIG. 1 shows a vertical pulverizer of this type. It has a vertical shell 1 which accommodates a vertical screw shaft 2 and is filled with pulverizing medium b such as steel balls. A material a is put into the shell 1 with the screw shaft 2 in rotation. The material a flows up and down together with the pulverizing medium b in the shell, so that it is pulverized into minute particles c by friction between individual pieces of the material and between the material and the medium. The particles c thus obtained are carried out of the shell 1 by a carrier fluid d such as air or water.
Due to the movement of the material and the pulverizing medium in the shell 1, its inner surface is subjected to a large frictional force. Thus, it is necessary to provide the inner surface of the shell with some kind of wear protective means. Such wear protective means are disclosed in Unexamined Japanese Patent Publication 5-329393 and Examined Japanese Patent Publication 44-29838. A wear protective means of the type disclosed in these publications is shown in FIG. 6. It comprises vertical ribs or rods 21 and circumferential ribs or shelf boards 22. Pulverizing medium trapped in the spaces defined by the ribs 22 and 21 covers and protects the inner surface of the shell 1 like a lining.
This wear protective means is constructed first by providing rods 21 to cover the entire length of a portion of the inner surface of the shell 1 that needs protection against wear. Then, shelf boards 22 and cylindrical sheaths 23 are fitted on the rods 21 from bottom to top. The rods 21, shelf boards 22 and sheaths 23 are made of a wear-resistant alloy, a wear-resistant rubber or a ceramic material.
Though the pulverizing medium b trapped in the protective structure serves as a wear protective lining, the shelf boards 22 and the sheaths 23 inevitably get worn gradually as the pulverizer is operated for a long time. When they are worn to a certain degree, they have to be replaced with new ones. For this purpose, all the shelf boards 22 and the sheaths 23 have to be removed from the rods from top to bottom, and then new shelf boards and sheaths have to be fitted on the rods from bottom to top. This work is extremely troublesome.
Thus, worn shelf boards 22 and sheaths 23 are often left unreplaced. But worn shelf boards 22 can come off easily, making it increasingly difficult to trap the pulverizing medium b to form a wear protective lining. Without the wear protective lining, the inner surface of the shell 1 will be worn so quickly that the shell 1 may be prematurely damaged to such an extent that it needs massive repairs.